So my suggestion was in relation to a mixed class booking, two separate tickets. Your choice of carrier in economy class BNE to SIN, followed by a separate business class ticket on a choice of a few carriers from SIN to Europe. Qatar, Vietnam Airlines, Sri Lankan, Finnair - all of them quite regularly discount business class from Asia and you'd be looking in the $2200-$2800 range (return). So that combined with your BNE-SIN you'd be comfortably in the $3500 range. But - it is separate tickets, so you need to allow plenty of time to connect in SIN in case the flights are delayed (you can't rely on a 60 or 120 minute connection).
All of those carriers have full flat beds on the long haul flights. Plus lounge access and whatever else. Most of Europe is covered.